The difficulty in this job was to position the parts inside the glass in a way that they don't distort too much.
To get a 'natural' transparency I had to move and rotate the light source and also the camera angle many times just slightly to get the effect I wanted.
And of course with each adjustment I had to check how it looked when rendered.
A little refraction distortion due to the glass effect is natural though.
I reduce it by adding a mix shader and using the glass shader and transparency shader and shift the slider until I've got the 'right' amount of refraction.
I you want a heavy glass refraction then use solidify and play with the thickness.